Automatic refresh for local Maildir's mail counts -- an attempt based on named pipes

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Dear Mr. Varshavchik, dear other Cone users,

it has been more than a year since I wrote about means to automatically
refresh Maildir's displayed mail counts
(https://sourceforge.net/p/courier/mailman/message/35577227/).

I have been running the patch proposed there ever since and it worked.
Still, during a discussion with a friend, I got convinced that signals
and multithreaded programs should really be avoided as much as possible.

As a result, I have thought of another way to interact with Cone for
triggering a refresh of mail counts and ended up with an approach based
on named pipes.

Unlike before, a write to the named pipe does not interrupt Cone and
is thus much safer.

However, I did not manage to have the named pipe polled at the same
location as other poll calls in Cone happen, because this always
resulted in either my file descriptor being ignored (when calling
`fds.push_back(myServer::pollFDForRefreshMessageCount)` in
myserver.C:192 only) or in an endless loop (when calling `push_back`
also in line 239 in the same file).

The attached patch thus implements polling in an own location which
means it only happens every `mailCheckInterval` (worst case: 300)
seconds.

My questions are now as follows:

 * Is the idea implemented by the attached patch safe enough to be
   included in Cone?

 * What can I do to have the polling mechanism which is already in
   use in Cone also poll my named pipe file descriptor such that mail
   counts are immediately updated?

Thanks in advance and Yours Sincerely
Linux-Fan


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--- cone-beforechg/cone/cone.C	2018-03-25 16:10:45.317386165 +0200
+++ cone-0.96.2.20180216/cone/cone.C	2018-03-25 17:41:34.671972832 +0200
@@ -429,6 +429,7 @@
 			 myServer **selectedServer)
 {
 	CursesHierarchy hierarchy_screen( &myServer::hierarchy, mainScreen);
+	myServer::setCursesHierarchyPointerForRefreshing(&hierarchy_screen);
 	
 	titleBar->setTitles(_("FOLDERS"), "");
 
@@ -474,6 +475,8 @@
 		*selectedFolder=hierarchy_screen.folderSelected;
 	if (selectedServer)
 		*selectedServer=hierarchy_screen.serverSelected;
+
+	myServer::setCursesHierarchyPointerForRefreshing(NULL);
 }
 
 void hierarchyScreen(void *dummy)
@@ -1025,6 +1028,8 @@
 		delete myServer::remoteConfigAccount;
 		myServer::remoteConfigAccount=NULL;
 	}
+
+	myServer::closePollFDForRefreshMessageCount();
 }
 
 //
@@ -1142,7 +1147,7 @@
 	int recover=0;
 	Macros macroBuffer;
 
-	while ((optc=getopt(argc, argv, "vrCc:")) != -1)
+	while ((optc=getopt(argc, argv, "vrCc:m:")) != -1)
 	{
 		switch (optc) {
 		case 'v':
@@ -1151,6 +1156,22 @@
 		case 'r':
 			recover=1;
 			break;
+		case 'm':
+			// try to delete if existent, ignore fail
+			unlink(optarg);
+			if(mkfifo(optarg, 0644) < 0)
+			{
+				perror("Failed to create FIFO");
+				exit(1);
+			}
+			int pipe;
+			if((pipe = open(optarg, O_RDONLY | O_NONBLOCK)) < 0)
+			{
+				perror("Failed to open FIFO for reading");
+				exit(1);
+			}
+			myServer::setPollFDForRefreshMessageCount(pipe);
+			break;
 		case 'c':
 
 			myServer::configDir=optarg;
diff -x config.status -x '*.log' -x .deps -x Makefile -x Makefile.in -Nrau cone-beforechg/cone/curseshierarchy.C cone-0.96.2.20180216/cone/curseshierarchy.C
--- cone-beforechg/cone/curseshierarchy.C	2018-03-25 16:10:45.301386438 +0200
+++ cone-0.96.2.20180216/cone/curseshierarchy.C	2018-03-25 17:08:13.627911893 +0200
@@ -985,6 +985,26 @@
 	me->processDeletedFolder(parent, deleted, updatedFolder);
 }
 
+bool CursesHierarchy::RefreshIterator::visit(Hierarchy::Folder* f)
+{
+	if(f != NULL && this->cs != NULL)
+		f->updateInfo(this->cs, true);
+	return true;
+}
+
+bool CursesHierarchy::RefreshIterator::visit(Hierarchy::Server* s)
+{
+	if(s != NULL)
+		this->cs = s->getServer();
+	return true;
+}
+
+void CursesHierarchy::refreshAllFolders()
+{
+	RefreshIterator iterator;
+	getHierarchy()->root.prefixIterate(iterator);
+}
+
 ///////////
 bool CursesHierarchy::processKey(const Curses::Key &key)
 {
diff -x config.status -x '*.log' -x .deps -x Makefile -x Makefile.in -Nrau cone-beforechg/cone/curseshierarchy.H cone-0.96.2.20180216/cone/curseshierarchy.H
--- cone-beforechg/cone/curseshierarchy.H	2018-03-25 16:10:45.321386096 +0200
+++ cone-0.96.2.20180216/cone/curseshierarchy.H	2018-03-25 17:10:14.744631348 +0200
@@ -61,6 +61,14 @@
 
 	};
 
+	class RefreshIterator: public Hierarchy::EntryIterator {
+	private:
+		myServer* cs = NULL;
+	public:
+		bool visit(Hierarchy::Folder* f);
+		bool visit(Hierarchy::Server* s);
+	};
+
 public:
 	friend class DrawIterator;
 
@@ -84,6 +92,7 @@
 	bool drawErase(Hierarchy::Server *server, bool doErase);
 	void visible(Hierarchy::Entry *e);
 
+	void refreshAllFolders();
 
 private:
 	bool drawErase(std::string str1, int col1,
diff -x config.status -x '*.log' -x .deps -x Makefile -x Makefile.in -Nrau cone-beforechg/cone/myserver.C cone-0.96.2.20180216/cone/myserver.C
--- cone-beforechg/cone/myserver.C	2018-03-25 16:10:45.313386233 +0200
+++ cone-0.96.2.20180216/cone/myserver.C	2018-03-25 19:51:51.585481655 +0200
@@ -23,6 +23,7 @@
 #include <fcntl.h>
 #include <pwd.h>
 #include <unistd.h>
+#include <poll.h>
 
 #include <iostream>
 
@@ -42,6 +43,9 @@
 extern void folderIndexScreen(void *);
 extern void hierarchyScreen(void *);
 
+struct pollfd myServer::pollFDForRefreshMessageCount = { -1, POLLIN, 0 };
+CursesHierarchy* myServer::cursesHierarchyForRefreshing = NULL;
+
 myServer::myServer(string name, string urlArg)
 	: serverName(name), url(urlArg), mailCheckInterval(300), server(NULL),
 	  currentFolder(NULL), hierarchyEntry(NULL)
@@ -281,6 +285,18 @@
 				break;
 			}
 		}
+
+		// TODO Code works but may refresh only every 300sec.
+		//      Could the polling happen within the other poll calls?
+		char buf[128];
+		if(myServer::pollFDForRefreshMessageCount.fd != -1 &&
+				poll(&myServer::pollFDForRefreshMessageCount,
+							1, 0) > 0 &&
+				read(myServer::pollFDForRefreshMessageCount.fd,
+							buf, sizeof(buf)) > 0 &&
+				myServer::cursesHierarchyForRefreshing != NULL)
+			myServer::cursesHierarchyForRefreshing->
+				refreshAllFolders();
 	}
 
 	statusBar->notbusy();
@@ -1032,3 +1048,24 @@
 
 	finishCheckingNewMail();
 }
+
+void myServer::setPollFDForRefreshMessageCount(int fd)
+{
+	myServer::pollFDForRefreshMessageCount.fd = fd;
+}
+
+void myServer::closePollFDForRefreshMessageCount()
+{
+	if(myServer::pollFDForRefreshMessageCount.fd != -1)
+	{
+		if(!close(myServer::pollFDForRefreshMessageCount.fd))
+			perror("Failed to close message count update file "
+			       "descriptor");
+		myServer::pollFDForRefreshMessageCount.fd = -1;
+	}
+}
+
+void myServer::setCursesHierarchyPointerForRefreshing(CursesHierarchy* h)
+{
+	myServer::cursesHierarchyForRefreshing = h;
+}
diff -x config.status -x '*.log' -x .deps -x Makefile -x Makefile.in -Nrau cone-beforechg/cone/myserver.H cone-0.96.2.20180216/cone/myserver.H
--- cone-beforechg/cone/myserver.H	2018-03-25 16:10:45.313386233 +0200
+++ cone-0.96.2.20180216/cone/myserver.H	2018-03-25 17:11:03.572938075 +0200
@@ -14,6 +14,7 @@
 #include "curses/timer.H"
 #include "myreadfolders.H"
 #include "certificates.H"
+#include "curseshierarchy.H"
 
 #include <string>
 #include <vector>
@@ -86,6 +87,9 @@
 	std::map<std::string, std::map<std::string, std::string>
 	> folder_configuration;
 
+	static struct pollfd pollFDForRefreshMessageCount;
+	static CursesHierarchy* cursesHierarchyForRefreshing;
+
 public:
 	bool updateServerConfiguration(std::string name, std::string value);
 	std::string getServerConfiguration(std::string name);
@@ -220,6 +224,10 @@
 	void addHierarchy(bool assignRows);
 	void showHierarchy();
 	void updateHierarchy();
+
+	static void setPollFDForRefreshMessageCount(int fd);
+	static void closePollFDForRefreshMessageCount();
+	static void setCursesHierarchyPointerForRefreshing(CursesHierarchy* h);
 private:
 	void addTopLevelFolders();
 	void addTopLevelFolder(std::string);

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